1. Field of the Invention
The present invention relates to an antitheft device applied to vehicles such as motor cars, motorcycles, motor ships, jet propulsion boats, etc., propelled by the driving force of an internal combustion engine, and more particularly, it relates to an antitheft device for a vehicle or the like capable of making re-collation of an ID code unnecessary at times such as when power is turned on again.
2. Description of the Related Art
In the past, in order to start the engine of a vehicle for instance, a key switch for engine starting is mechanically turned on by means of an original or qualified cylinder key which has been passed only to an authorized driver of the vehicle concerned. As a result, the starting of the engine becomes impossible without the qualified key, whereby theft of the vehicle can be prevented. However, even if the anti-theft of the vehicle is intended to be prevented by means of the qualified key alone, it is not necessarily able to provide a satisfactory anti-theft effect because it is relatively easy to reproduce the original or qualified key.
Thus, in recent years, there is proposed, for example, the following system for the purpose of strengthening such an anti-theft effect. That is, information for specifying a key dedicated to a vehicle concerned is sent from the key to a corresponding key cylinder of the vehicle so that the information sent from the key can be identified or verified at the key cylinder side, and only when the information is regular or qualified information, the starting of the vehicle engine is permitted (for instance, see a first patent document: Japanese examined patent application publication No. H04-15141).
In an antitheft device for a vehicle described in the above-mentioned first patent document, concretely speaking, an annular core is arranged around a key insertion hole in a key cylinder of the vehicle concerned, and a key coil wound on an axial core inside the key is placed in proximity of a rotor coil wound on the annular core to form a couple of magnetic circuits, through which information for driving the vehicle engine can be transmitted between the key and the key cylinder.
As described above, the conventional antitheft device for a vehicle depends solely upon information transmissions between the key and the key cylinder through the magnetic circuits. Therefore, when a power supply in the vehicle is interrupted instantaneously, it is necessary to reexecute the process of sending key identification information from the key to the key cylinder and the process of verifying the key identification information at the key cylinder side in a repeated manner, thus giving rise to a problem that information transmissions between the key and the key cylinder take time, thereby creating the possibility of causing trouble or impediment to the operation of the vehicle during traveling.
Particularly, in cases where equipment for sending key identification information from the key to the key cylinder has failed during traveling of the vehicle, generating an instantaneous interruption, there arises another problem that the vehicle gets stopped and becomes unable to continue traveling, making it impossible to arrive at a destination.